Planographic printing plates

ABSTRACT

An improved planographic printing plate based upon a polyvinyl alcohol binder material in the printing layer. The improvement resides in the incorporation of a certain amount of zinc oxide, relative to the amount of polyvinyl alcohol, in order to provide a printing layer which has an excellent hydrophilic-oleophilic balance, excellent ink-drying properties and avoids spreading of the oleophilic images on the plate surface.

United States Patent Inventor Douglas A. Newman Glen Cove, NJ.

Appl. No. 795,047

Filed Jan. 29, 1969 Patented July 13, 1971 Assignee Columbia Ribbon andCarbon Mnnuheturlng Cm, lne. Glen Cove, NY.

I'LANOGRAPHIC PRINTING PLATES JChIIns, NoDrlvIlnas U.S.CI. .r 101/462,101/457, ll7/l38.8, 117/155, 260/296, 260/41 Int. Cl B4ln 1/00, B4ln3/00 FleldotSeu-ch 101/457,

Primary Examiner-Morris Liebman Assistant Examiner-J. l-l. DerringtonAttorney-Johnson and Kline ABSTRACT: An improved planographic printingplate based upon a polyvinyl alcohol binder material in the printinglayer. The improvement resides in the incorporation of a certain amountof zinc oxide, relative to the amount of polyvinyl aloohol, in order toprovide a printing layer which has an excellent hydrophilic-oleophilicbalance, excellent ink-drying properties and avoids spreading of theoleophilic images on the plate surface.

PLANOGRAPHIC PRINTING PLATES This invention relates to the art ofplanographic printing plates of the polyvinyl alcohol type whichrepresent a marked improvement over prior art plates of this type withrespect to ink-drying characteristics and resistance to spreading orbroading of the oleophilic images applied to the plate surface.

Polyvinyl alcohol plates of the type described in Perkins U.S. Pat. No.3,055,295 and other patents have enjoyed widespread commercial successfor several reasons including their ease of production. Such plates havea self-insolubilizing formulation due to the presence therein of apolyfunctional organic hardener which reacts with the water-solublepolyvinyl alcohol to insolubiliae it and render it more oleophilic. Thebinder material is a hydrolyzed polyvinyl alcohol and is commerciallyavailable as a dilute aqueous solution such as under the trademarkElvanol.

The polyvinyl alcohol planographic compositions also contain colloidalsilica and large amounts of clay which assist in providing the requiredhydrophilic-oleophilic balance. However the most important ingredient isthe hardener. Without this material, the polyvinyl alcohol will notinsolubilize sufficiently and will not accept or retain oleous images tothe required extent.

The problems presented by hardened polyvinyl alcohol plates relate tothe slow drying of oleous images typed onto such plate surfaces and theresultant image spread due to the migration of the liquid ink from theimages into adjacent areas of the plate surface. By the time the imagesdry completely, which takes several days, the images are much broaderthan originally typed.

Attempts to overcome these problems by increasing the amount of hardenerand filler provide some improvement by rendering the planographic layermore oleophilic and more porous. However the necessary hydrophilicproperties of the layer are disturbed with resultant toning, stop-startcharacteristics, and the like.

It is the object of the present invention to overcome the inkdrying andimage-spread problems of polyvinyl alcohol planographic layers withoutdisturbing the necessary hydrophilic properties to produce plates havingexcellent stop start characteristics, resistance to toning, quick inkdrying and resistance to image-spreading.

These and other objects and advantage of this invention will be clear tothose skilled in the art in the light of the present disclosure.

According to the present invention, l have discovered that plates havingexcellent ink-drying properties and excellent hydrophilic-oleophilicbalance can be produced by adding to the planographic composition anamount of zinc oxide powder which is in excess of the amount ofpolyvinyl alcohol and which is equal to not substantially more thanabout one-half the amount of clay filler present. It is not clear howthe zinc oxide functions to provide the novel and unexpected resultsobtained. However this specific material, when used in the amountindicated, improves the hydrophilic properties of the planographic layerwhile at the same time giving it the ability to dry oleous images in amatter of a few minutes whereby image-spreading is prevented.

The novel planographic compositions of the present invention comprisewater, polyvinyl alcohol binder material, colloidal silica, hardener orinsolubilizing agent, clay and zinc oxide. Other conventionalingredients are also preferably included such as dispersing agents,catalysts, pH adjusting agents, and the like.

The colloidal silica is a material such as commercially available underthe trademarks Ludox or Syton 200 and is present in an amount in excessof the polyvinyl alcohol and up to about four times the weight ofthepolyvinyl alcohol. The colloidal silica functions somewhat as a binder,aftlldfitiidhii insoiubilizing agent for the polyvinyl alcohol. Howeveran amount of a different polyfunctional hardener or insolubilizing agentis also required. Aldehyde donors aredpreferred such as methylol ureasand methylol melamtnes an other urea-or melamine-formaldehyde lowpolymers conventionally-used for this purpose. Glyoxal is less preferredbecause of its reactivity and instability, and IS preferably used onlyin combination with another hardener of the aforementioned type. Thehardener is present in an amount equal to from about 10 per cent up toabout 120 percent of the amount of polyvinyl alcohol, i.e. in a ratiooffrom l:l0 up to l .211.

Clay is an essential ingredient of the present compositions and is usedin excess of the amount of polyvinyl alcohol in a ratio of from about3:1 up to about l0: 1.

The zinc oxide is the ingredient which unexpectedly improves theproperties of the planographic layer with respect to ink-drying andimage-spreading. The zinc oxide, however, must be used in combinationwith the other ingredients and in the amount indicated. The ration ofzinc oxide to polyvinyl alcohol ranges from above lzl up to 5:1. Thelatter proportion is only possible where the ratio of clay to polyvinylalcohol is lOzl.

It should be understood that the present plate formulations may beapplied over conventional water-barrier layers and/or hydrophilicunderlayers which improve the operation and correction properties of theplates. Coatings of this type are conventional in the planographicprinting art. Similarly, the flexible foundation sheet may be a plasticfilm where the plates are intended for use in the thermographic andphotographic fields.

The following Examples are given by way of illustration of suitableplanographic compositions which can be coated onto a conventionalflexible foundation in conventional manner to provide plates having thenovel characteristics enumerated.

[Parts by weight] E samples Ingredients:

Polyvinyl alcohol 2. 0 2. 0 2. 0 Sytonmt](40%auue0us)........ 15.0 11.815.0 Glyoxal (40? aqueous) 0. 5 1. 5 2. 0 Methyloluted melamine resin 0.5 0. 6 l. 0 Clay 15. 5 11.5 18. 0 Zinc oxide. 8. 0 4. 0 8. 0 Acetic acid0. 2 0. 2 0.2 Zine acetate (25% aqueous) 3. 5 4. 0 3. ll Aluminumsulphate (10% aqueous)... 8.0 9. 0 8.0 Butyl alcohol 0.7 0. 5 0. B'Irisodium pyrophosphate 0. 05 0. 06 0. 06 Water 46. 05 54. 42. 45

Total 100. 00 100.00 100. 00

For comparison purposes, compositions can be produced according to theforegoing Examples in which the total combined amount of clay and zincoxide is replaced with an equal amount of clay alone or zinc oxidealone. Modified compositions of this type are unsatisfactory in thatplates produced therefrom do not have satisfactory stop-gocharacteristics or ink-drying properties and the images spread orbroaden thereon. Similarly, the replacement of clay or zinc oxide withequal amounts of fillers heretofore regarded as equivalent materials,such as barium sulfate, titanium dioxide, calcium oxide, or the like,results in plates which do not have the sub stantially instantaneousink-drying properties of the present formulations and have poor stop-gocharacteristics.

lclaim:

1. Planographic printing plate having fast ink-drying properties andresistance to spreading of oleophilic ink images applied to the printingsurface thereof which comprises a flexible foundation supporting ahydrophilic planographic printing layer having a hydrophilic-oleophilicbalance comprising 1 part by weight of polyvinyl alcohol bindermaterial, a polyfunctional hardening agent reacted with said polyvinylalcohol to cause its insolubilization, more than 1 part by weight ofcolloidal silica, from 3 to 10 parts by weight of clay and from morethan i to 5 parts by weight of zinc oxide, said zinc oxide being presentin a weight not substantially more than about one-half the weight ofclay present.

2. Printing plate according to claim 1 in which the hardening agent ispresent in a weight equal to from (H to 1.2 times the weight of thepolyvinyl alcohol.

3. Printing plate according to claim 2 in which the hardening agentcomprises an aldehyde resin.

2. Printing plate according to claim 1 in which the hardening agent ispresent in a weight equal to from 0.1 to 1.2 times the weight of thepolyvinyl alcohol.
 3. Printing plate according to claim 2 in which thehardening agent comprises an aldehyde resin.